The "methods" published in the early days of the piano - each virtuoso wrote his own - dwelt on the importance of stillness. JB Cramer (or Glorious John, as he was known in London) was famed for his immobility. Clementi made his pupils practise with a coin on the back of their hands. Mozart, who prided himself on making his music flow "like oil", believed the fingers should always be in close contact with the keys. Machines were invented to keep arms and hands clamped in the "correct" horizontal position. Beethoven, who broke pianos the way Pete Townshend broke guitars, was a lone pioneer in the art of histrionic arm-waving.
But by the beginning of the 19th century, the penny was beginning to drop: piano-playing could be sexy. Ladislav Dussek, possessor of a strikingly noble profile, was the first to insist on being seen side-on. People began to savour the poetry of motion. John Field, who left his native Dublin for stardom in St Petersburg, sent the Russian composer Mikhail Glinka into ecstasies: "His fingers, like great drops of rain, poured over the keys as pearls on velvet."
One observer described the way Chopin's hands "would suddenly expand and cover a third of the keyboard. It was like the opening of the mouth of a serpent, about to swallow a rabbit whole." But Chopin was anything but flamboyant. "He kept his elbows close to his sides, and played only with finger touch - no weight from the arms," recalled a London piano- maker. "He used a simple, natural position of the hands." But when the eye-rolling, mane-tossing, mesmerising Liszt burst on the scene, the game was raised for good.
The video screen now used for recitals at the Queen Elizabeth Hall reflects the perennial desire to both hear and see: even from the back of the auditorium you can watch the fingers in close-up. But Gianluca Cascioli, the 16-year- old Italian who acted as guinea-pig last Sunday, also demonstrated the system's limitations. The most interesting visual aspect of his playing was the way he hovered over the keys, as though controlling the sound after his fingers had done their bit. But this was beyond the scope of the camera.
If a camera were to be focused on the keyboard at the Barbican this Sunday, the screen would be largely blank. Only the widest of angles could convey the physicality of Olli Mustonen's playing - hands raised high over head, feet flying out at angles, his whole body in a dance. At first sight this can be distracting, and it is this, as much as his wayward tempi, that has divided the critics.
But this 27-year-old Finn is in many ways extraordinary. Precocious both as a performer and a composer, he was dubbed at 12 his country's Mozart; in his early twenties he was running festivals. His manner is quick and nervy: as he talks, he gestures constantly with pale, delicate hands and he seems instinctively combative.
He defends his keyboard manner before I've even got round to challenging it. The subject surfaces during a discussion of his early hero, the Russian virtuoso Emil Gilels. "Just seeing his hands - like the paws of a bear - was inspiring to me. Now, if I find something I am playing problematic, I think back to how he might have played it - and how it would have looked. If I watch a pianist on TV, I can tell how it's sounding even if the sound is switched off. With Gilels you could see that it sounded beautiful."
"A pianist has to be a magician: he has to create the illusion of continuous sound, when in reality - unlike string or wind players - he only plays the beginning of each note. Although it must never sound like that - and it will not, with a pianist like Gilels. He made it sound as natural as singing."
"There is an analogy with tennis players, whose rackets only give the first impulse to the ball. But even at my lowly level of tennis, I get the feeling of living through the whole movement of the ball, the follow- through. Great tennis players don't use jerky movements, they play with big, natural movements, taking into account the laws of gravity and the pendulum. The same applies to piano playing.
"To move from a note here to a note there, the hand will go like this" - and he describes a graceful arc over the table. "You might think the most economical route would be this" - hand shooting across like a piston - "but it's not. It makes you tense. You must use gravity. It may sound silly, but piano playing is less to do with hitting the keys, than with lifting them up. You are playing between the moments when you hit the notes." All of which begins to make sense.
How does he react to criticisms? "I don't read them. People have a right to say what they think. I have a right to my own peace of mind. It may sound pompous, but I believe in what I am doing."
Listening to him talk - or to his compositions, marked, even in his teens, by a beguilingly expressive purity - you sense that he has never doubted himself. Growing up in a house full of harpsichords and spinets, he got off to a flying start. He remembers the moment when, after despairing of deciphering the hieroglyphs of a score, "it suddenly came together like a puzzle. This music here" - pointing to an imaginary score - "and here" - his head - "and here" - his hands - "was one and the same thing. A revelation! I was five."
With his elder sister he developed a game called The Composition Office. "We made forms, and customers came in and commissioned work - a certain length, for a certain instrument, sonatas and symphonies. And we would deliver them, with a letter signed by the director." He dislikes the "unhealthiness" of the concert circuit, crams his tours into the winter months, and spends the summer composing in the farmhouse he shares with his pianist wife.
On Sunday at the Barbican he will play Beethoven's Triple Concerto. The cellist will be Stephen Isserlis, who is one of his closest buddies. Another close friend, with whom he and Isserlis frequently form a trio, is the American violinist Joshua Bell. On occasion, Mustonen and Bell make a duo, whereon hangs a tale that they have both, at different times, told me the same way.
They were once due to play Beethoven's Kreutzer Sonata but, in rehearsal, things went wrong: they disagreed absolutely on the tempo of the slow movement. "Either I would have had to compromise, or he would have," said Bell. "Which would have bred resentment," Mustonen added. "It would have been wrong for either of us to follow the requirements of the other." So they aborted the project.
Bell also admitted that he had had to develop a much bigger sound to match Mustonen's powerful delivery. I am reminded of this as Mustonen muffles up - it's a warm day - and folds those delicate hands into a giant pair of strangler's leather gloves, before going off to practise.
n Olli Mustonen plays Beethoven's Triple Concerto, with the LSO, conducted by Richard Hickox: Sun 7.30pm Barbican, London EC1. Booking: 0171-638 8891Reuse content